This invention relates in general to the processing of semiconductor chips and packages and in particular, to a system for controlling an integrated production process for the processing of semiconductor wafers and packages.
After a semiconductor wafer has been fabricated, it undergoes a series of processing steps before the finished product in the form of semiconductor chip packages are shipped to customers. First, the semiconductor wafer is handled by a prober or sorter in conjunction with a tester for testing the electrical properties of the dies on the wafer, in order to sort the bad dice from the good ones. Typically, the good dice are put in bins separate from bins for the bad dice, in a process called binning. Thereafter, the wafers are cut into separate dice and each individual good die is then enclosed within a package. Semiconductor packages are then handled by a handler in conjunction with a tester to again test the electrical properties of the dies within the packages. The second round of testing is necessary since the packaging process may have damaged the dice contained in the packages or the leads of the package.
To improve overall yield, it is important to collect data at each stage of the above-described process to make sure that the equipment used for testing and processing is properly set up, calibrated and functioning normally, and to discover possible problems in the fabrication process of the wafers. For this purpose, various control systems have been proposed.
Thus, a control system sold by KLA Instruments Corporation of San Jose, Calif., for controlling probers or sorters sold by the same company, enables operators to analyze wafer test results. The capabilities of the KLA control system include compilation of individual and composite wafer result maps that show the frequency of dies passing or failing, and creation of control maps indicating which dies to ink, skip or test. Typically, the dice failing to pass the test are marked by ink dots. The control system supplied by KLA Instruments employs a network where a number of cell controllers are connected by an Ethernet network, where each cell controller is used to control a test cell, which in turn may include a number of probers. The network system enables operators more flexilibity in creating and editing wafer setup files and control maps, and for monitoring the status of different probers.
Triage Corporation of Hillsboro, Oreg. supplies a control system employing a network where a number of cell controllers are connected by an Ethernet network, where each cell controller is used to control a test cell, which in turn may include a number of Electroglas probers. The network system enables operators more flexilibity in creating and editing wafer setup files and control maps, and for monitoring the status of different probers.
LTX of Westwood, Mass., has made available a distributed network workstation system for controlling and monitoring the status of a number of testers and for collecting and analyzing data from the testers.
Thruput Systems Inc. of Mesa, Ariz., has commercialized a system for controlling test equipment; in a product brochure from Thruput Systems, it is stated that the Thruput system monitors test heads from different testers as well as handlers. The system provides fixed format product test time reports and handler assembly reports.
Among the systems described above, the control systems provided by LTX and KLA Instruments are each compatible only with the probers, testers or handlers provided by the same company and not compatible with equipment from any other company. The control systems provided by Thruput Systems and Triage appear to be compatible only with specific equipment. From the point of view of overall test production management, it would be desirable to be able to control and monitor the status of testers, sorters and handlers on the test floor and collect data therefrom for yield analysis during production. Since the above-described types of control systems may not be compatible with equipment provided by some manufacturers, it is difficult to adopt any one of the systems for monitoring the whole test floor. This is particularly the case where, as is true for many integrated circuit manufacturers, equipment from different manufacturers are used on the test floor. In other words, an operator on a typical test floor would have to physically attend to each computer controlling each individual piece of equipment in order to control and monitor the status of the equipment, and collect data therefrom for analysis. Even if one of the above-described systems is used, the operator would still have to attend to a system for monitoring probers and may still need to attend to a different system for monitoring testers. The lack of uniformity and overall control means that an operator would have to keep track of a large number of procedures and factors.
The above-described problems due to the lack of an overall production management tool are compounded in the applications specification integrated circuit (ASIC) environment. The ASIC manufacturer manufactures wafers and packages in accordance with different specifications from a number of customers. Each specification may call for a different setup or equipment for testing and processing. For example, different printed circuit boards would have to be used for testing wafers and packages with different specifications. According to the experience of one integrated circuit manufacturer, about ten thousand printed circuit boards would have to be kept in stock and maintained at any time for testing wafers and packages. These printed circuit boards are kept in a storage and retrieval unit called a carousel, a system monitored and controlled by means of a personal computer. The personal computer enables an operator to keep track of the boards, including their preventive maintenance schedules. Thus, when a wafer manufactured in accordance with the particular specification is to be tested, information on the printed circuit board required by the specification would have to be fetched so as to determine the appropriate printed circuit board to be used for testing. Such board would then be retrieved from the storage and retrieval unit or carousel with the aid of the personal computer. The printed circuit board is then used in conjunction with a wafer sorter (or prober) and a tester for testing the electrical properties of the wafer. The printed circuit board is then returned to the carousel. The number of times the same board has been used may need to be monitored in order to perform preventive maintenance.
After the wafer has been cut into different dies and packaged, the packages are then handled by the handlers and tested using the testers again in conjunction with a specified printed circuit board. For the above-mentioned integrated circuit manufacturer, a host VAX computer is used as the primary control and computational platform for the sort, test and mark/pack areas. This computer stores and loads all production test programs and buffers all set up information from computer-aided manufacturing node for automatic station configuration and real-time yield monitoring. It carries out yield computations and maintains all electrical and mechanical statistical process control data for all testers, sorters, handlers and lead inspection systems. It also controls through the personal computer the use of the printed circuit boards from the storage carousel.
Tester, sorter/handler manufacturers usually sell control stations together with the testers, sorters/handlers. Such control stations, however, are not compatible with other computers such as VAX computers. Thus, the host VAX computer cannot communicate directly with the control stations for the testers, probers and handlers sold together with such equipment by the manufacturers. Therefore, an additional computer must be used at each tester, prober or handler location to be the interface between the control device for a particular tester, sorter or handler, and the host VAX computer. In order to operate a tester, sorter or handler, an operator must first retrieve a production program from the host VAX computer, using the additional computer at the location at the piece of equipment, perform any interface procedures required with a control device in order to implement the production program for such equipment, Typically, the control terminal for a particular tester, sorter or handler has its own syntax and configuration, so that an operator would have to know such syntax and configuration in order to implement the production program on such equipment.
Since a sorter (prober) or handler must communicate with a tester in order for the two pieces of equipment to coordinate the handling and the testing of wafers and packages, an electronic interface register (EIR) cable is used to connect the sorter (prober) or handler to the tester. However, as indicated above, no control system is available which can be used to control a sorter as well as a tester, an operator would have to control and monitor individually the tester and the sorter connected to it by the EIR cable using the control monitors for the tester and the sorter. Even though the signals transmitted through the EIR cable contain important information on the performance of the tester and sorter or handler and the tested device, presently available control systems do not take advantage of such information.
None of the above-described systems is entirely satisfactory. It is therefore desirable to provide an improved system for controlling an integrated production process for semiconductor chips and packages in which the above-described difficulties are eliminated or reduced.